Alarm for Gateway Firewall TCP Half-Open Flow Count High

Products

• VMware vDefend Firewall
• VMware vDefend Firewall with Advanced Threat Prevention
• VMware NSX Firewall

Issue/Introduction

Products: VMware NSX Firewall / VMware vDefend Firewall

Title: Alarm for gateway_firewall.tcp_half_open_flow_count_high

Event ID: gateway_firewall.tcp_half_open_flow_count_high

Added in release: 3.1.3

 

Alarm Description:

Purpose: The gateway firewall flow table usage for TCP half-open traffic is high.

Impact:  New flows will be dropped by Gateway firewall when usage reaches the maximum limit. The maximum limit is set through the flood protection profile applied on the gateway.

Environment

VMware NSX-T Datacenter

VMware NSX

Resolution

• Log in as the admin user on Edge node and invoke the NSX CLI command `get firewall <INTERFACE_UUID> interface stats  | json` by using right interface uuid and check flow table usage for TCP half-open flows.
• Use the NSX CLI command `get firewall <INTERFACE_UUID> connection state' and check the number of connections for a given interface.
• Check traffic flows going through the gateway is not a DOS attack or anomalous burst. If the traffic appears to be within the normal load but the alarm threshold is hit, consider increasing the alarm threshold or route new traffic to another Edge node.